1. Field
This patent specification relates to a method and apparatus for optical disc recording, and more particularly to a method and apparatus for high-speed optical disc recording using an MCM (multi chip module).
2. Discussion of the Background
Currently, various types of information (for example, not only general computer information but also information of sounds, still images, moving images, and the like) are digitalized. As a result, the amount of information processed by computer is increased. As a medium for recording the variety of information, an optical disc such as a DVD+RW/+R is widely used.
Data is written on the optical disc by applying a laser beam thereto and forming a recording pit thereon. When the data is written on the optical disc, a drive current based on a write pulse having a predetermined pulse width is applied to a semiconductor laser of an optical pickup. The semiconductor laser then applies a laser beam to a recording surface of the optical disc rotating at a predetermined speed.
FIG. 1 is a block diagram illustrating a common system configuration of an optical disc recording apparatus for writing data on the optical disc. In the optical disc recording apparatus 100 of FIG. 1, an optical disc 101 is a recordable disc such as a DVD+RW/+R and a CD-R. A spindle motor 102 rotates the optical disc 101. A disc controller 103 controls driving of the spindle motor 102 according to a CLV (constant linear velocity) method, wherein a rotation speed of the optical disc 101 becomes inversely proportional to a radius of a track of the optical disc 101. That is, in recording data on and reproducing data from the optical disc 101, a linear velocity is controlled to be constant at any radial position of the track. Accordingly, the spindle motor 102 drives to rotate the optical disc 101 at a constant speed. Further, the disc controller 103 controls the driving of the spindle motor 102 such that the spindle motor 102 controls the rotation of the optical disc 101 by a PLL (phase locked loop) method, wherein the optical disc 101 is rotated at a predetermined speed, for example, a normal speed, a 2×-speed (i.e., two-time speed), a 4×-speed, an 8×-speed, a 12×-speed, and so forth.
An optical pickup 104 includes a semiconductor laser, an optical system, a photo-detector, and so forth (not shown) for focusing and applying a laser beam to the optical disc 101 to perform data recording or data reproduction. In data recording, the optical system focuses the laser beam emitted from the semiconductor laser and applies a beam spot to a recording surface of the optical disc 101, so that a recording pit is formed on the recording surface. In data reproduction, the recording surface is applied with a laser beam having a lower power than a power used in the data recording. Then, a light reflected from the recording surface is focused by the optical system, subjected to an optical-to-electrical conversion at the photo-detector, and output from the optical pickup 104 in a form of a reproduced signal.
An encoder 105 performs predetermined data processing such as interleaving and error check coding on data to be recorded on the optical disc 101, and modulates the data by EFM (eight-to-fourteen) modulation or ESM (eight-to-sixteen) modulation to generate a modulated signal for the data recording. The encoder 105 then sends the modulated signal to a strategy generation circuit 106. The strategy generation circuit 106 generates a write pulse having a predetermined pulse length in consideration of a write strategy parameter, and sends the generated write pulse to an LD (laser diode) driver 107. The LD driver 107 then generates a drive current for driving the semiconductor laser of the optical pickup 104, based on the write pulse received from the strategy generation circuit 106. As a result, the optical pickup 104 applies the laser beam to the optical disc 101 with a predetermined power according to the write pulse.
A servo controller 108 controls focusing and tracking of the laser beam emitted from the semiconductor laser of the optical pickup 104. The servo controller 108 performs the tracking control by detecting a pregroove formed on the recording surface of the optical disc 101. A R/F (radio frequency) circuit 109 performs a predetermined operation on a waveform of the reproduced signal transmitted from the optical pickup 104, and generates an FE (focusing error) signal indicating a deviation of the beam spot from the recording surface and a TE (tracking error) signal indicating a deviation of the beam spot from a predetermined track. The generated FE signal and TE signal are used at the servo controller 108 for controlling the focusing and tracking of the laser beam. The R/F circuit 109 further performs a predetermined operation on the waveform of the reproduced signal transmitted from the optical pickup 104 and binarizes a resultant signal to generate an R/F signal. A decoder 110 demodulates the R/F signal by EFM demodulation or ESM demodulation to generate demodulated data, and performs data processing such as error correction and deinterleaving. An ATIP (absolute time in pregroove) decoder 111 demodulates the TE signal transmitted from the R/F circuit 109 to generate a wobble signal. At the ATIP decoder 111, noise components are eliminated from the TE signal by a band-pass filter (not shown), and the TE signal is digitalized by a binarization circuit (not shown) and demodulated by an FSK (frequency shift keying) demodulation circuit (not shown), so that the wobble signal is generated. The disc controller 103 controls the rotation of the optical disc 101 such that the wobble signal takes a predetermined value.
The demodulated wobble signal contains CRC (cyclic redundancy check) data to be used for error checking. The CRC data is checked to find if data has been correctly read out. Data of a wobble signal read error ratio (hereinafter referred to as ATER (ATIP error rate)) is stored in a resistor provided in the ATIP decoder 111 during a data reproduction operation and updated every predetermined time period.
A system controller 112 including a CPU (central processing unit) reads the data of the error ratio stored in the register to monitor the ATER during a data recording operation. The system controller 112 forms, together with the ATIP decoder 111, main parts of a wobble signal read error measuring unit that measures the ATER during the data recording operation. The system controller 112 controls, in accordance with a command transmitted from an external apparatus such as a personal computer, respective circuit blocks of the disc controller 103, the encoder 105, the strategy generation circuit 106, the LD driver 107, the servo controller 108, the R/F circuit 109, and so forth, such that data is recorded on or reproduced from a predetermined sector of the optical disc 101. A host I/F (interface) 113 is an interface for communicating the optical recording apparatus 100 with a host machine such as a personal computer so that commands and data are transmitted between the optical recording apparatus 100 and the host machine.
The data to be recorded on the optical disc 101 is input from the external apparatus in the encoder 105 via the host I/F 113. As described above, the data thus input is subjected to the predetermined processing such as the interleaving and the error check coding and then to the EFM modulation or the ESM modulation, so that the write pulse having the predetermined pulse length in consideration of the write strategy parameter is generated by the strategy generation circuit 106. During the data recording operation, the ATER is checked at regular time intervals. If it is detected that the ATER has exceeded a predetermined value, a width of the write pulse is reduced to be a slightly shorter than a write pulse width usually used. Further, to obtain an original pit length, a write power is increased immediately before falling of the write pulse to compensate for the reduced width of the write pulse. The write pulse is then input in the LD driver 107 to generate a drive current according to a length of the pit to be formed on the recording surface of the optical disc 101. The drive current is input in the optical pickup 104 to drive the semiconductor laser, and the laser beam emitted from the semiconductor laser is focused by the optical system to form the beam spot on the recording surface of the optical disc 101 rotating at the constant speed. Accordingly, a pit having a predetermined length is formed on the recording surface.
As illustrated in FIG. 2, LSIs (large-scale integrations) forming circuit blocks of the optical disc recording apparatus 100 are mounted on printed circuit boards, i.e., a main circuit board 120 for controlling the system of the optical disc recording apparatus 100, and a pickup board 130 connected to the main circuit board 120 by a flexible cable 140. The main circuit board 120 is mounted with a control LSI 121 for forming the above circuit blocks forming the system of the optical disc recording apparatus 100 shown in FIG. 1, i.e., the disc controller 103, the encoder 105, the strategy generation circuit 106, the servo controller 108, the R/F circuit 109, the decoder 110, the ATIP decoder 111, the system controller 112, and so forth. The LSIs for forming the circuit blocks are formed by a plurality of chips but denoted by the control LSI 121 as one circuit block in FIG. 2. The pickup board 130 is reduced in size so as to move integrally with the optical pickup 104, and is mounted with an LD driver chip 131 forming the LD driver 107.
PS (power supply) LSIs 122, 123, and 124 for supplying power voltages are mounted on the main circuit board 120 to reduce the size of the pickup board 130 as much as possible. In FIG. 2, the three PS LSIs 122, 123, and 124 are used for different purposes, for example, for supplying a voltage of 5 V to drive the semiconductor laser, a voltage of 3.3 V to be used for the host I/F 113 communicating the optical disc recording apparatus 100 with an external apparatus, and a voltage of 1.8 V to perform digital processing in the optical disc recording apparatus 100.
A speed of recording data on the optical disc has been increased from the normal speed to a 2×-speed, a 4×-speed, an 8×-speed, and so forth. In fact, the applicant of the present patent application has already been marketing an optical disc recording apparatus performing 2.4×-speed data recording on a DVD+RW/+R and 12×-speed data recording on a CD-R (e.g., a product sold under the trademark MP5125A).
In this circumstance, there is an increasing demand for an optical disc recording apparatus capable of recording data on the optical disc at a further faster recording speed. For example, there is a demand for a faster data recording speed on a DVD, such as a 16×-speed and a 32×-speed. To increase the data recording speed, a speed of signal processing such as strategy generation should be increased. The conventional optical disc recording apparatus configured to transmit signals obtained through the strategy generation to the pickup board via the flexible cable, however, has a limitation in increasing a signal transmission speed due to such influences as noise. It is therefore difficult to increase the data recording speed on the DVD.
To address the above, a digital signal arithmetic LSI and an LD driver LSI, which form the strategy generation circuit, may be integrated and mounted on the pickup board. The digital signal arithmetic LSI and the LD driver LSI can be integrated by a technique of MCM, wherein a plurality of LSIs are incorporated in one package. The MCM has an advantage that the plurality of LSIs forming different circuits such as a memory circuit, a logic circuit, and an analog circuit are integrated in one package to provide a high-performance, multi-functional system device.
The above-described strategy generation circuit is a digital signal arithmetic circuit, and the LD driver is an analog signal arithmetic circuit. An LSI forming the strategy generation circuit and an LSI forming the LD driver can be integrated by using the MCM technique. Since the strategy generation circuit should perform a high-speed operation, it is preferable that the strategy generation circuit is highly integrated and driven at a relatively low voltage. Conversely, the LD driver should be driven at a relatively high voltage for driving the semiconductor laser, for example, at 5 V.
As described above, the conventional pickup board 130 is not mounted with any PS LSI, and therefore a predetermined power voltage is supplied via the flexible cable 140 from the main circuit board 120 to an individual circuit mounted on the pickup board 130.
In the configuration of the conventional optical disc recording apparatus 100, however, if the LSI forming the digital signal arithmetic circuit and the LSI forming the LD driver are integrated to form the strategy generation circuit and mounted on the pickup board 130 to receive predetermined power voltages via the flexible cable 140, the following disadvantage is caused, impeding increase in the signal processing speed.
That is, in the conventional configuration supplying the predetermined power voltages via the flexible cable 140 to the respective LSIs mounted on the pickup board 130, an unintended impedance is generated in a PS (power supply) LSI due to parasitic inductance (L) and capacitance (C) caused by wiring of the printed circuit boards or the flexible cable 140. When a current consumed by the LSI, i.e., a load of the PS LSI receiving power from the PS LSI is changed over time due to the impedance, an output power characteristic of the PS LSI, as well as a load change characteristic specific to the PS LSI, may be deteriorated.
The impedance of the power output from the PS LSI refers to, in this example, a characteristic impedance of the wiring of the PS LSI. Generally, the characteristic impedance is expressed as in the formula of Z=(L/C)1/2. It is determined from the formula that the impedance can be decreased by increasing the capacitance or by decreasing the inductance. The capacitance can be increased by inserting a bypass capacitor between a ground terminal GND and a power supply terminal of the LSI serving as a load, or by increasing a width of the wiring line. The inductance may also be decreased by increasing the width of the wiring line. Increase in the width of the wiring line, however, leads to increase in area of the printed circuit board, which is not acceptable from a viewpoint of downsizing of the printed circuit board. Therefore, the output power characteristic is conventionally improved by inserting a variety of filters in a power supply line. In an optical disc recording apparatus operating at an increasingly faster speed, however, this technique of inserting the filters does not satisfactorily work for effectively driving the write strategy circuit and the LD circuit.
Further, as the operational speed of the optical disc recording apparatus with respect to the DVD increases, density of data recorded on and reproduced from the DVD is increased. As a result, the speed and accuracy of a signal processed by an LD driver chip continues to be improved. Particularly, the accuracy in time of a recording signal becomes an important factor for increasing the data writing speed on the DVD. The accuracy in time of the recording signal is determined by oscillation accuracy of a PLL (phase-locked loop) circuit, which is included in the digital signal arithmetic LSI of the strategy generation circuit, and which generates a reference clock signal for a modulated signal used for the data recording on the DVD. A jitter of the PLL circuit should be reduced to improve data writing accuracy and the data writing speed.
The jitter of the PLL circuit includes a random jitter caused by such factors as a thermal noise and a deterministic jitter having a specific frequency component. The random jitter largely depends on a process of manufacturing the circuit, and thus it is difficult to reduce the random jitter by modifying a configuration of the PLL circuit. Conversely, the deterministic jitter often occurs when a noise having a specific frequency is superposed on power supply lines (VCC) and ground lines (GND) provided in a circuit board. The noise superposed on the power supply lines (VCC) and the ground lines (GND) is triggered by the above-described impedance occurring in the wiring of the PS LSI and by operation of the load circuit.
As described above, to increase the data recording speed on the DVD, the oscillation accuracy of the PLL circuit included in the digital signal arithmetic LSI should be improved.